This section presents an overview of the findings presented in the preceding eight chapters. As noted in chapter 1, this overview emphasizes areas in which significant problems are likely to arise; that is, those situations which could, under certain conditions, pose a threat to the well- being of the spacecrew or to the success of the mission.
Chapter I, LIVING IN SPACE, presents an introduction to issues of human adaptation to space and outlines the basic assumptions underlying our approach to this topic. This chapter also  provides an overview of the basic psychological and interpersonal consequences of isolation and confinement. These conditions often have been found to result in Impaired intellectual functioning, motivational decline, somatic disturbance, psychological changes, and social tensions, the latter being reflected in a tendency to withdraw from fellow confinees and to react in a hostile manner toward outsiders. Withdrawal among isolated and confined individuals frequently is accompanied by a pattern of depression which peaks approximately two-thirds of the way through the confinement experience.
Chapter II, BEHAVIORAL AND SELECTION IMPLICATIONS OF BIOMEDICAL CHANGES, examines behaviors which may change as a result of physiological alterations coincident with space travel. Although physiological responses to space and to environments simulating space are relatively consistent, behavioral measures taken under the same simulation conditions generally have failed to demonstrate consistent effects. However, the possibility of genuine behavioral effects cannot be excluded. The present lack of consistent response differences may reflect an insufficient sensitivity of measuring instruments or the presence of characteristics in the experimental environment which permit the individual to focus on the task in a way that would not be possible in the more demanding environment of space.
There appears to be a number of important psychophysiological variables that relate to an individual's ability to adapt to spaceflight. For example, space sickness or space adaptation syndrome affects about one-half of all space travelers, primarily during the early days of a mission. Earth-based studies, although far from conclusive, suggest that psychophysiological correlates, including age, gender, and personality traits, could be predictive of an individual's susceptibility to space sickness. Sensory conflict theory continues to be helpful in directing research efforts in the general understanding of why space sickness occurs and how to simulate it on Earth. Psychophysiological correlates have proven helpful in determining adaptability to other spaceflight conditions. For example, one intriguing line of evidence suggests that the highly athletic individual may present no advantage in withstanding the effects of weightlessness and may even be at a disadvantage compared with an average, healthy individual. Similarly, there is evidence to suggest that older individuals may handle certain types of physiological stress better than younger ones. These and related findings could have important selection implications.
 In chapter III, HABITABILITY, we note the need for a shift in emphasis from merely sustaining human life in space to maintaining a high quality of life in space. To accomplish this shift, it is necessary to broaden our perspective to include not only such obvious issues as environmental integrity and safety, sanitation, and nutrition, but also such subtle issues as environmental richness, temperature and humidity, and compatibility among crewmembers. The use of leisure time is a significant habitability issue. Confined individuals tend to place heavy emphasis on assigned work and little emphasis on recreational opportunities. When recreation is sought, it tends to be passive in nature. Although exercise is needed to meet many of the health requirements of space, exercise programs have not been pursued enthusiastically by space travelers.
Privacy, for the group as well as for the individual, has been identified as a significant issue for extended spaceflight. Many of the privacy mechanisms used on Earth are lacking in space. Of the privacy devices that remain to the space traveler, manipulation of the interior space and decor and training in the regulation of the sharing of information about oneself appear to offer the greatest hope for privacy protection.
In chapter IV, PERFORMANCE, we consider demands placed on spacecrews to accomplish mission objectives. Work schedules are influenced by workload demands, sleep requirements, stress, and many other variables. In space, work capacity can be altered by changes such as increased metabolic requirements, and by other conditions of weightlessness such as difficulty in moving from one location to another. Both difficulty in sleeping and the necessity for sudden awakening can contribute to performance decrement. Individuals show performance decrement throughout the day; therefore, the circadian rhythms themselves have implications for establishing work schedules. Desynchronosis, the result of changes in circadian rhythms produced by artificial environments, can contribute to performance decrements in space. Changes in work and sleep schedules can produce symptoms similar to those of jet lag. In space, when performance decrements occur, fine motor skills appear to be more negatively affected than gross motor or cognitive skills.
Aside from the earliest days of Mercury and Vostok, spaceflight has been a shared venture. In chapter V, SMALL GROUPS, we note that a clear understanding of interpersonal dynamics is important for mission success. Groups whose members lack compatibility have  been found to have lowered morale, increased stress, decreased motivation, and, when the opportunity is present, a high rate of member loss. In assembling a crew, it is necessary to consider how the qualities of different people interplay. Complementary needs, similar values and attitudes, and a strong but noncompetitive work orientation are among the qualities that are thought to contribute to social compatibility. Groups can be aided by the inclusion of individuals who are personally attractive, competent, and who can respond both to the demands of the task and to the needs of others. People who are similar to each other appear to have a compatibility advantage, at least in the short term, but bringing together individuals differing in age and social and cultural backgrounds, and of both sexes is likely to enrich the confinement experience over time.
Leadership is presumed to be a major factor in the effectiveness of spacecrews. Although leadership is often thought of as a quality of the individual, leadership depends on three sets of characteristics: characteristics of leaders, characteristics of followers, and characteristics of situations and tasks. Leadership is associated with two types of activities: task and socioemotional. Autocratic decision making appears to have an advantage when expertise is concentrated in the hands of the leader and when speed in decision making is important. Democratic procedures can lead to better decisions when expertise is distributed across group members and when it is desirable for all to have a high degree of commitment to the decision.
There are many ways in which spaceflight conditions are likely to affect dynamics within small groups. Historically, members of isolated and confined groups have had difficulty containing interpersonal conflict without resorting to social withdrawal. Direct training in interpersonal relations may be of some help in this regard. In isolated and confined groups, conformity and compliance pressures are likely to be high; this can make it difficult for individuals to offer creative solutions to problems. Conformity pressures can result in the rejection of the nonconformist, a result which may be unacceptable under spaceflight conditions. Established groups would seem to offer some advantages for long-duration missions. Ideally, a crew entering space would be sufficiently "old" that its members will have achieved a high degree of interpersonal coordination, but sufficiently "young" that they will not have become bored with one another. Space stations and other space environments that are likely to have crews of rotating membership will have to grapple with the problem of assimilating new members into the crew.
 In chapter VI, COMMUNICATION, we note some of the ways that conditions of spaceflight influence the transmission of information from person to person. Within the spacecraft, propulsion and life-support equipment are noisy and could interfere with verbal communication. Nonverbal communication may be hampered by distortion of facial expressions and distancing cues associated with weightlessness. Among the most significant communication issues for space are those involving contact between people aboard the spacecraft and people who are on the ground or aboard another space vehicle. Mediated communication systems must be developed to meet the needs of the crew throughout an extended mission. Under Earth conditions, mediated systems are generally used to handle formal, businesslike, and routine exchanges, tasks which they do well. In space, mediated systems will have to handle all communications needs - personal and subtle, as well as impersonal and straightforward. Systems designs for space must take into consideration people's emotional requirements as well as their requirements for information exchange. To this end, the use of video is promising.
Among the problems of formal communication networks are barriers to information flow. One such barrier is the tendency for individuals at all levels to impede the upward flow of negative or disconcerting information. In addition, some strategically located individuals known as gatekeepers have particular power to influence the flow of information throughout the group or organization. In space, heavy reliance must be placed on formal communication arrangements, for instance between the spacecrew and mission control, since informal communication networks will be difficult or impossible to establish.
Precipitous events affecting either the physical safety or the psychological well-being of the crew are discussed in chapter VII, CRISES IN SPACE. The spacecrew must be prepared to deal with both physical threats and the emotional responses to such threats. Some evidence suggests that fear can be managed by learning to control the timing of the fear experience. Effective handling of a threatening situation will require that organizational arrangements and procedures be in place prior to the occurrence of the event. Following recovery from a threat, it is possible that, in space as elsewhere, blaming or scapegoating will occur.
Other occurrences that could cause a serious disturbance on-board include a severe psychiatric event or the death of a crewmember or a loved one at home. Isolation and confinement may  contribute to depression and other forms of psychological distress and, on rare occasions, psychotic episodes have been observed in environments having some of the characteristics of space. In maintaining the mental health of space travelers, success in the work role and maintaining good relationships with other crewmembers will be of primary importance. Also of concern are the immediate reactions to the death of another and the predictable, but disruptive, reactions associated with grief.
In chapter VIII, ORGANIZATION AND MANAGEMENT, we note that large spacecrews will take on the characteristics of complex organizations. Informally evolved means of achieving interpersonal coordination will be supplemented, if not replaced, by externally imposed rules and regulations, and structural considerations will come to the fore. Social structure is reflected in the distribution of authority and tasks. The multileveled hierarchy is the most common form of authority structure. However, alternate models exist and their application to space deserves careful consideration. The Russians report success in using hierarchical methods to make determinations regarding the technical and performance aspects of a mission; however, they found democratic methods to be more appropriate for making determinations regarding life within the spacecraft. Centralization of authority is desirable to the extent that central authorities have good communication with remote units and a good understanding of their situation. However, as missions last longer and become more remote from Earth, the effectiveness of Earth-based, centralized authority may decline. Truly large crews will require leadership at many different levels. Middle-level and top-level Ieaders may require managerial capabilities above and beyond those required to successfully lead the relatively small crews associated with the space missions of today.
Future spaceflights are likely to be marked by pressures toward increased specialization. Among the work roles that are likely are flight operations, scientific-investigative, environmental support, personnel support, and production roles. Formal roles that are specified in advance by mission planners and managers will tend to be supplemented or even replaced by emergent or informal roles. Role-related conflicts could emerge. Some roles may be seen as more important than others, and occupants of certain roles may form blocs or factions which are antagonistic to other groups. A suggestion for extended spaceflight is that individuals be rotated across roles; among other benefits, this practice could foster tolerance by breaking down status distinctions and helping crewmembers to gain each  other's perspective. Role rotation also could encourage creative problem solving and introduce welcome changes of pace into an otherwise monotonous routine.
In chapter VIII, we also consider the motivational forces that attract people to organizations and encourage dependable role performance. Certain extrinsic rewards are expected to lose force under tomorrow's spaceflight conditions. Pay may lose incentive value, since money cannot be spent freely in space. Furthermore, as space travel becomes common, another important extrinsic satisfaction- social recognition-will decline. Little is known about how sanction systems might work in space, but it seems likely that the usual punishments (fines, incarcerations, etc.) will not be practical or effective. To some extent, the expected decline in the availability of extrinsic satisfactions might be offset by increases in the availability of intrinsic satisfactions. Such satisfactions tend to be high when work is available that taps personal skills, provides autonomy, and is consistent with both personal and superordinate goals.
Many isolation studies have revealed overt hostility between crewmembers and external monitors or authorities. Although there is general agreement that conflict can have a functional aspect, damaging conflict between organizational units such as a crew and mission control needs to be prevented or at least contained. Persons who serve as interfaces between the crew and other groups or organizations play a critical role in determining the presence or course of intergroup hostility.